Hybrid electric vehicles offer reduced fuel consumption by utilizing an internal combustion engine and one or more electric motor/generators as commanded by an onboard controller programmed to vary use of each of the engine and motor/generators during different driving conditions to achieve peak efficiency.
An extended-range electric vehicle is a hybrid electric vehicle that is designed to provide consistent electric-only drive performance as the energy storage system (ESS) is depleted during drive. The ESS is typically a battery or battery pack for a hybrid electric vehicle. Since ESS power capability varies as a function of the state-of-charge of the ESS during discharge due to the variation of open circuit voltage and cell resistance in the ESS, the ESS must be sized to meet the power requirements at the minimum state-of-charge and lowest temperature at which it is desired that the vehicle is capable of operating in electric-only operating mode. The level of ESS and electric drive power capacity overdesign due to this sizing strategy depends in large part on the amount of variation in battery pack voltage and resistance. Vehicles designed for an increased electric-only operating range may use energy dense batteries, which tend to have an increase in variation in voltage over the battery discharge cycle, and higher resistance.